166 Mineralogical Characterization of Economic Resources: From Critical Minerals to Gemstones

From ore materials to precious gemstones, minerals play an important role in almost every aspect of our lives. This session will focus on characterization of economic minerals employing spectroscopic techniques, geochemical analysis, and microanalytical techniques.

Tuesday, 21 October 2025
8:00 AM - 12:00 PM
HBGCC, 217A

Improved Identification of Kimberlitic Zircons Using Trace-Element Compositions and Machine Learning: Implications for the Search for Superdeep Diamonds

Paper number: 166-10
Program: Technical Sessions
Time: 10:30 AM – 10:45 AM

Authors

  • Matthew Hardman Presenting Author
    Gemological Institute of America, Carlsbad, California
  • D. Graham Pearson
    University of Alberta, Earth & Atmospheric Sciences, Edmonton, Alberta
  • S. Andy DuFrane
    University of Alberta, Earth & Atmospheric Sciences, Edmonton, Alberta
  • Izaac Cabral-Neto
    Geological Survey of Brazil - SGB/CPRM, Natal, Rio Grande do Norte
  • Rogério Azzone
    Institute of Geosciences, University of São Paulo, São Paulo, São Paulo
  • Qiao Shu
    University of Alberta, Earth & Atmospheric Sciences, Edmonton, Alberta
  • Jason Hinde
    University of Alberta, Earth & Atmospheric Sciences, Edmonton, Alberta
  • Alexei Rukhlov
    BC Geological Survey, Victoria, BC

Abstract

Zircon is an important pathfinder mineral for identifying igneous source rocks, including kimberlite and carbonatite. However, discrimination of zircons from these two lithologies is challenging due to their surprisingly limited published trace element data and their compositional overlap. Kimberlites can be diamond-bearing, and in rare cases these diamonds may be sourced from the sublithospheric mantle. Such diamonds are often sought after due to their size and purity. Consequently, enhanced tools to identify kimberlite deposits containing superdeep diamonds can provide new value to diamond exploration practices.

Here we determined the trace-element compositions of 170 new zircon megacrysts from kimberlites and of 220 new zircons from global carbonatites and related rocks. The kimberlitic zircon megacrysts in the present study have a relatively narrow range of trace-element compositions whereas the new carbonatite zircons are compositionally diverse and likely reflect formation under varied geological conditions from a variety of heterogeneous sources, as well as complex equilibrium mineral assemblages. We have also compiled zircon trace-element compositions for a wide variety of rocks from published literature (including from crustal rocks), allowing for more general classification approaches.

We apply random forest and discriminant projection analysis to distinguish zircons from kimberlite and carbonatite from those in many crustal lithologies. Both approaches can discriminate kimberlite-related zircons from those in other host rocks, with error rates as low as 8.5±10.0% (2σ). We further apply our database to evaluate whether there is a compositional fingerprint that can distinguish zircon megacrysts from kimberlites containing superdeep diamonds from those that do not. While we find broad separation between subsets of zircon from kimberlites with and without superdeep diamonds using our preliminary dataset, more compositional data for zircons from known superdeep-diamond-bearing kimberlites are necessary to evaluate any possible compositional fingerprint. These new data do, however, allow broader investigation of the petrogenesis of zircon megacrysts in kimberlites.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-413685

© Copyright 2025 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.